1. Field of the Invention
The invention relates to a storage apparatus which comprises a plurality of storage media such as HDDs and, more particularly, to a storage apparatus which has an unused physical area autonomous management function of creating a virtual logical disk, and assuring a physical area in correspondence with an actual use size.
2. Description of the Related Art
Conventionally, in a storage apparatus which comprises storage media such as HDDs to configure an array, a correspondence between a logical volume in which a host apparatus which uses the storage apparatus accesses a subsystem that manages the array, and the array configured by one or more storage media that define that logical volume is fixed, and the ratio of an area which is not used as the logical volume in practice becomes high, resulting in a large waste.
Hence, a virtual logical disk system which manages a physical area by segmenting the physical area into extents each having a predetermined size, and actually assures an extent in which a write access to the logical volume has occurred has been developed (http://www.3par.com/products/thinprovisioning.html (storage product available from 3PARData, Inc., U.S.A.)).
However, such a virtual logical disk system suffers the following problems.
That is, with a storage apparatus of this type, if a storage area which was used once but becomes available as a new data allocation again as a result of deletion of files or that of a partition can be released, a physical storage area can be used more efficiently.
However, with this virtual logical disk system, there is no standard scheme for explicitly communicating an area which becomes unused or available again in a file system of a host apparatus to a storage apparatus. For this reason, communicating new-unused sectors from the host apparatus to the storage apparatus and managing management information of these unused sectors on the storage apparatus side lead to a huge management information size. Also, since management information is checked every disk access, the system performance may deteriorate (problem 1).
As for an area becomes unused again and an area in which data has never been written of the logical disk in use, data of a physical area can be read by issuing a read request from a layer lower than the file system to the storage device as a physical disk. For this reason, when a plurality of users can access an identical logical disk or when a physical extent previously used by a certain user is allocated to a logical disk used by another user, data of a deleted sector area and unused sector area are read from a storage, resulting in a risk of information leakage to ill-intentioned users and the like (problem 2).